Alkaline storage battery

Abstract

An alkaline storage battery in which an actual reaction area is not reduced after increasing a reaction area is provided. A hydrogen storage alloy negative electrode 11 of an alkaline storage battery 10 of the present invention is formed in a strip form including a long axis and a short axis, in which the ratio (A / B) of a length A (cm) of the long axis to a length B (cm) of the short axis is 20 or more and 30 or less (20≦A / B≦30), and the ratio (X / Y) of an electrolyte volume X (g) retained in the hydrogen storage alloy negative electrode 11 to an electrolyte volume Y (g) retained in a separator 13 is 0.8 or more and 1.1 or less (0.8≦X / Y≦1.1). With this arrangement, an alkaline storage battery with high output characteristics and long-term durability performance is obtained.

Description

TECHNICAL FIELD[0001]The present invention relates to an alkaline storage battery suited to applications requiring high-current discharge such as hybrid electric vehicles (HEVs) and pure electric vehicles (PEVs). More particularly, the invention relates to an alkaline storage battery including an electrode group fabricated by rolling a positive electrode using nickel hydroxide as a main positive electrode active material and a hydrogen storage alloy negative electrode using a hydrogen storage alloy as a negative electrode active material into a spiral form with a separator that keeps the two electrodes apart interposed therebetween, an alkaline electrolyte, and an outer can inside which the foregoing items are housed.BACKGROUND ART[0002]In recent years, alkaline storage batteries, especially nickel-hydrogen storage batteries, have been used for an electric current source for vehicles such as HEVs or PEVs. Long-term durability performance such as high output performance far beyond th...

AI Technical Summary

Benefits of technology

[0010]An advantage of some aspects of the invention is to provide an alkaline storage battery which has excellent output characteristics and improved self-discharge characteristics by employing a battery structure in which an actual reaction area is not reduced when increasing a reaction area.

[0018]Here, the hydrogen storage alloy containing a rare earth element, magnesium, and nickel as primary elements includes a combination of an AB2 type structure with the AB5 type structure, thereby forming an A2B7 type structure or the A5B19 type structure. In this case, the A5B19 type structure is a pile-up of a cyclic trilayer including the AB2 type structure and the AB5 type structure that enables the nickel (Ni) proportion per unit crystal lattice to be increased compared with the A2B7 type structure.

[0019]An increase in the nickel (Ni) proportion per unit crystal lattice enables an active point that accelerates adsorption and desorption of hydrogen to be increased, thereby improving high-output characteristics. In addition, hydrogen storage alloy containing rare earth element, magnesium, and nickel as primary elements includes a combination of the AB2 type structure and the AB5 type structure that are mediated by magnesium, thereby removing manganese and cobalt.

[0020]Therefore, by using an alkaline storage battery which is made to have a reaction area between positive and negative electrodes far beyond conventional level using such hydrogen storage alloy, both high output characteristics and long-term durability performance can be achieved.

[0021]According to the invention, a reaction area between a positive and negative electrode is increased by optimizing the ratio of a long axis length to a short axis length, and an electrode group constitution that increases an electrolyte mass retained to a hydrogen storage alloy negative electrode is employed. With this arrangement, an alkaline storage battery with high output characteristics and long-term durability performance is obtained.

Problems solved by technology

In this case, a value of the above-mentioned positive electrode area less than 30 cm2 / Ah does not reduce the internal resistance of the electrode group, leading to a decrease in an operating voltage and difficulty in attaining a high current discharge.

However, even if a reaction area is increased as proposed in the above-mentioned JP-A-2000-082491 and JP-A-2007-294219, the following other two problems emerge.

A first problem is that there is a region in which no improvement of output characteristics is recognized even after increasing a reaction area.

This reduces an actual reaction area of the electrode plate, leading to no improvement of output characteristics.

A second problem is that using an AB5 type hydrogen storage alloy used in general as a negative electrode active material as a negative electrode plate with an increased reaction area is found to cause a degradation of self-discharge characteristics (an increase in self-discharge).

This accelerates self-discharge, leading to degradation of self-discharge characteristics.

In this case, increasing an electrolyte mass retained in the negative electrode plate to solve the first problem causes further elution of manganese and cobalt, leading to marked degradation of self-discharge characteristics.

When the ratio (A / B) of the length (A) of the long axis to the length (B) of the short axis of the hydrogen storage alloy negative electrode is less than 20 (A / B<20), it is found that a reaction area between a positive and negative electrodes cannot be increased, leading to no improvement in output characteristics.

In addition, even when the ratio (A / B) of the length (A) of the long axis to the length (B) of the short axis of the hydrogen storage alloy negative electrode is 20 or more, it is found that output characteristics cannot be fully improved with a small electrolyte mass retained in the hydrogen storage alloy negative electrode.

Meanwhile, when the ratio (A / B) of the length (A) of the long axis to the length (B) of the short axis of the hydrogen storage alloy negative electrode is more than 30 (A / B>30), the thickness of each of electrodes and separators should be reduced, leading to difficulty in preparing from a point of view of a strength.

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